PRT: Mass Transit Without the "Mass"

Imagine instead of a single huge bus, all these
empty seats could run around separately (or in sets of 2, 3 or 4), picking up
people on-demand and transporting them non-stop to their destinations. The
result would still be MASS transit, except now it would be individualized  or
PERSONAL.

We're all familiar with conventional transitlarge vehicles that run on
timetables, stopping at designated locations. Show up at the appointed place,
hope the system is running on schedule, and you and a lot of other people ride
the route together. The primary problem with this type of mass transit is
that the "mass" is mostly vehicle mass, not people mass.

PRT turns the conventional formula on its head. PRT begins from the
observation that automobiles don't operate on timetables, so why should
transit? By running when YOU want to travel (demand-responsive, or
"on-demand"), PRT takes the large groups of bus or train riders and
spreads them out over time, like this:

Same numbers of people, but in PRT they get to travel
at their convenience, and the ride is private or with others of their choice. Is this
efficient? Yeswith PRT, vehicles only move when someone needs one. Buses and
trains have to keep to their schedules even when partially fulland even when
empty. Is PRT cost effective? Yesthree buses might cost $500,000 each. In the
above table of 41 PRT trips, the 65 people could be served by only 10 PRT
vehicles costing $10-20,000 each.

Only 10!? Because PRT doesn't force everyone to travel together,
each of the 10 vehicles can pick up riders, drop them off, then pick up more. This sharing
of vehicles by riders in succession is the key to PRT's total carrying capacity, and
it's possible because service is on-demand.

One PRT vehicle can make 5, 6, or even more separate journeys per hour, depending upon
average trip length. But because PRT travels nonstop at 20-45 mph the entire way,
each trip will usually be short. Thus, if one vehicle makes 6 trips per hour...

# vehicles

Trips per hour

20

120

100

600

500

3,000

5,000

30,000

If we assume an average of 1.2 persons per trip (about the same
as cars), the 5,000 vehicle fleet can have a maximum hourly ridership level of
36,000 people, or 864,000 per day. For comparison, consider that (at this writing)
total weekday bus ridership for all of King County averages about 330,000.